Camshaft-in-camshaft apparatus of variable valve duration system

ABSTRACT

A camshaft-in-camshaft apparatus may include a hollow outer shaft having at least one slot formed along a length direction of the hollow outer shaft, an inner shaft rotatably inserted inside the outer shaft and having at least one pin hole formed on the inner shaft, a position of each of the at least one pin hole corresponding to that of each of the at least one slot, one or more first cam lobes fixedly mounted on an exterior circumference of the outer shaft, one or more second cam lobes fixedly mounted on the inner shaft to be rotatable on the corresponding slot of the outer shaft, a cam phaser changing a phase angle between the outer shaft and the inner shaft by rotating any one of the outer shaft and the inner shaft, and at least one torsional spring mounted between any one of the one or more first cam lobes and any one of the one or more second cam lobes.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority of Korean Patent Application Number 10-2013-0160726 filed on Dec. 20, 2013, the entire contents of which application are incorporated herein for all purposes by this reference.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to a camshaft-in-camshaft apparatus, and more particularly, to the camshaft-in-camshaft apparatus of variable valve duration system that a torsional spring is applied to.

2. Description of Related Art

An internal combustion engine generates power by flowing fuels and air into combustion chambers and combusting them. For combustion, an intake valve is opened by a driving camshaft and while the intake valve is opened, the air flows into the combustion chamber. Further, an exhaust valve is opened by the driving camshaft after combustion and while the exhaust valve is opened, combustion gas is discharged out of the combustion chamber.

Optimum operation of an intake valve or an exhaust valve is adjusted depending on rotating speed of an engine. This is because adequate valve lift or valve opening and closing time varies depending on the engine rotation speed.

Like this, the way of varying opening or closing time of an intake valve or an exhaust valve in accordance respectively with low speed or high speed of an engine in order to supplement the general drawbacks thereof is called variable valve timing (VVT) method.

Unlike a prior camshaft, a camshaft-in-camshaft comprises a hollow camshaft, namely an outer shaft and a different shaft inserted therein, namely an inner shaft. A camshaft-in-camshaft structure has been devised so that among two types of valve connected thereto, a first type of valve is moved invariably in line with engine timing without special control and the movement of a second type of valve is controlled in order for the phase of the valve to become different from that of the first type of valve.

By this, continuous variable valve timing (CVVT) method can be realized. Continuous Variable Valve Duration (CVVD) method can also be realized, using a camshaft-in-camshaft apparatus.

In general, an engine with CVVD realized has two intake valves and two exhaust valves in a combustion chamber, one of cam lobes driving two valves of the same kind is connected with an outer shaft of the camshaft-in-camshaft, and the other cam lobe is connected with an inner shaft thereof so that those two cam lobes are respectively and independently movable with each other.

The same kind of two valves of a combustion chamber can respectively have different valve opening or closing times and valve durations are variable as a result if an outer shaft and an inner shaft are connected with a hydraulic pressure type of variable valve control apparatus, relative motions of them are generated, and thereby the phases of two valves of the same kind become different. That is, an opening time of intake valves or exhaust valves, namely valve duration can be varied.

In case two intake valves or two exhaust valves have the same phase, a minimum opening time is generated and in case the difference in the phase is maximum, a maximum opening time is generated. Intake valves or exhaust valves have a minimum opening time in the default position of variable valve duration.

When CVVD method is realized with a camshaft-in-camshaft apparatus, closing time of an intake valve may happen to be too delayed because a maximum opening time could be larger.

In case closing time of an intake valve is too delayed like particularly in early stage of engine ignition or in time of stopping an engine, startability could be very deteriorated because effective compression ratio reduces on account of a lengthened overlap with an exhaust valve opening time.

The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

SUMMARY OF INVENTION

Various aspects of the present invention are directed to providing a means of making a camshaft-in-camshaft apparatus used in CVVD system rapidly return to its original position and thereby minimizing the overlap of an intake valve opening time and an exhaust valve opening time in order to secure startability of an engine.

According to various aspects of the present invention, a camshaft-in-camshaft apparatus may include a hollow outer shaft having at least one slot formed along a length direction thereof, an inner shaft rotatably inserted inside the outer shaft and having at least one pin hole formed thereon, a position of each of the at least one pin hole corresponding to that of each of the at least one slot, one or more first cam lobes fixedly mounted on an exterior circumference of the outer shaft, one or more second cam lobes fixedly mounted on the inner shaft to be rotatable on the corresponding slot of the outer shaft, a cam phaser changing a phase angle between the outer shaft and the inner shaft by rotating any one of the outer shaft and the inner shaft, and at least one torsional spring mounted between any one of the one or more first cam lobes and any one of the one or more second cam lobes.

A first cam hole may be formed at any one of the one or more first cam lobes and a second cam hole may be formed at any one of the one or more second cam lobes. Both ends of one or each of the at least one torsional spring may engage respectively with the first cam hole and the second cam hole.

According to various other aspects of the present invention, a camshaft-in-camshaft apparatus may include a hollow outer shaft having at least one slot formed along a length direction thereof, an inner shaft rotatably inserted inside the outer shaft and having at least one pin hole formed thereon, a position of each of the at least one pin hole corresponding to that of each of the at least one slot, one or more first cam lobes fixedly mounted on an exterior circumference of the outer shaft, one or more second cam lobes fixedly mounted on the inner shaft to be rotatable on the corresponding slot of the outer shaft, and a cam phaser changing a phase angle between the outer shaft and the inner shaft by rotating any one of the outer shaft and the inner shaft, wherein the cam phaser includes a stator connected to one of the outer shaft and the inner shaft and a rotor connected to the other of the outer shaft and the inner shaft, and a torsional spring is mounted between the stator and the rotor.

According to some aspects of the present invention, a first fixing part may be formed or mounted on the stator and a second fixing part may be formed or mounted on the rotor, and both ends of the torsional spring may be fixed to or engaged respectively with the first fixing part and the second fixing part. The first fixing part may be a clamp screwed to the stator and the second fixing part may be a fixing groove formed in the rotor.

The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary camshaft-in-camshaft in which a torsional spring is mounted according to the present invention.

FIG. 2 is a cross-sectional view of an exemplary camshaft-in-camshaft in which a torsional spring is mounted according to the present invention.

FIGS. 3A and 3B are drawings which show a perspective view and a rear view of an exemplary cam phaser in which a torsional spring is mounted according to the present invention.

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings.

In addition, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements and the name of a component doesn't set limits to the function of the component concerned.

FIG. 1 is a perspective view of a camshaft-in-camshaft in which a torsional spring is mounted according to various embodiments of the present invention. FIG. 2 is a cross-sectional view of a camshaft-in-camshaft in which a torsional spring is mounted according to various embodiments of the present invention.

A camshaft-in-camshaft apparatus according to various embodiments of the present invention may comprise an outer shaft 1, an inner shaft 2, one or more first cam lobes 3, one or more second cam lobes 4, a cam phaser 5 (Refer to FIGS. 3A and 3B), and a torsional spring 6.

The outer shaft 1 is a hollow shaft on which at least one slot is formed along its length. In some embodiments, two slots are symmetrically formed at a point of the outer shaft 1 with respect to a rotation axis of the outer shaft 1.

The inner shaft 2 may be rotatably inserted inside the outer shaft 1 and at least one pin hole 12 may be formed on the inner shaft 2, a position of each pin hole 12 corresponding to that of each slot so that a fixing pin 20 can be inserted through them.

One or more first cam lobes 3 are fixedly mounted on an exterior circumference of the outer shaft 1. A first cam hole 13 may be formed at any one of the first cam lobes 3.

One or more second cam lobes 4 are fixedly mounted on the inner shaft 2 so as to be rotatable on the corresponding slot of the outer shaft 1. The second cam lobes 4 may be fixed to the inner shaft 2 by a fixing pin 20 (Refer to FIG. 2).

The fixing pin 20 may be slid through the one fixing hole 15 on a flange of the second cam lobe 4, the slot on the one side of the outer shaft 1, and the pin hole 12 of the inner shaft 2 in order, continuing through the axis of rotation of the inner shaft 2 and the slot on the other side of the outer shaft 1 to the other fixing hole 15 on the opposite side of the flange of the second cam lobe 4. The fixing pin 20 may fix the second cam lobe 4 to the inner shaft 2 by being tightly fitted to the fixing hole 15 of the second cam lobe 4 and the pin hole 12 of the inner shaft 2. In contrast, it may make a clearance fit to the outer shaft 1 through the slot so that the second cam lobe 4 can rotate back and forth on the slot of the outer shaft 1.

However, the fixing method is not limited only in that way.

A second cam hole 14 may be formed at any one of the second cam lobes 4.

The cam phaser 5 is configured such that the cam phaser 5 can change a phase angle between the outer shaft 1 and the inner shaft 2 by rotating any one of the outer shaft 1 and the inner shaft 2.

Accordingly, phase difference is generated between the first cam lobes 3 rigidly attached to the outer shaft 1 and the second cam lobes 4 rigidly attached to the inner shaft 2 and rotating back and forth on the corresponding slots of the outer shaft 1, valve timing between two intake valves or two exhaust valves actuated by a first cam lobe 3 and a second cam lobe 4 is variable, and thereby duration (an opening time) of intake valves or exhaust valves can be varied.

The torsional spring 6 is an elastic member providing a rotating body with restoring force in the opposite direction of rotation. Both ends of the torsional spring 6 according to some embodiments of the present invention may engage respectively with the first cam hole 13 and the second cam hole 14.

The operational principle of the torsional spring 6 is as follows.

In case the cam phaser 5 makes the outer shaft 1 rotate, and thereby the first cam lobes 3 rotate relatively with respect to the second cam lobes 4, duration of valve opening time can be varied. As the relative rotating displacement happens by the relative rotating motion, the torsional spring 6 generates restoring force in the opposite direction of the displacement.

If an engine is stopped or just started, oil of hydraulic pressure control apparatus gets out, and thereby only the restoring force generated by the torsional spring 6 acts between the first cam lobes 3 and the second cam lobes 4. So, the first cam lobes 3 and the second cam lobes 4 get back to their default starting angular position and valve duration is initialized. As a result, intake valves are opened within a minimum opening time and the valve overlap is minimized such that startability of the engine improves.

In case the cam phaser 5 makes the inner shaft 2 rotate, and thereby the second cam lobes 4 rotate relatively with respect to the first cam lobes 3, only the direction of the restoring force generated by the torsional spring 6 is reversed and the effect of getting back is the same. That is, the intake valves are opened within a minimum opening time and the valve overlap is minimized such that startability of the engine improves.

FIGS. 3A and 3B are drawings which show a perspective view and a rear view of a cam phaser in which a torsional spring is mounted according to various embodiments of the present invention. Referring to FIGS. 3A and 3B, cam phaser 5 according to various embodiments of the present invention may comprise a stator 7 connected to one of the outer shaft 1 and the inner shaft 2 and a rotor 8 connected to the other of the outer shaft 1 and the inner shaft 2.

Therefore, if a torsional spring 6 can be mounted between the stator 7 and the rotor 8, the same effect as both ends of the torsional spring 6 are mounted between any one of the first cam lobes 3 and any one of the second cam lobes 4 may be generated. This is because restoring force in accordance with the relative rotating displacement between the outer shaft 1 and the inner shaft 2 is eventually generated.

A clamp 9 may be mounted in the stator 7 according to some embodiments of the present invention and a fixing groove 10 may be formed in the rotor 8.

FIGS. 3A and 3B show a condition in which one end of the torsional spring 6 is caught in the anticlockwise direction with respect to a rotation axis and the other end thereof is inserted and fixed in the fixing groove 10.

In case the rotor 8 is in relative motion of rotating anticlockwise with respect to the stator 7, valve timing or duration of valve opening time can be varied and restoring force by the torsional spring 6 is generated in the opposite direction of the motion.

If an engine is stopped or just started, oil of hydraulic pressure control apparatus gets out, and thereby only the restoring force generated by the torsional spring 6 acts between the stator 7 and the rotor 8.

So, one of the outer shaft 1 and the inner shaft 2 connected to the stator 7 and the other connected to the rotor 8 get back to their default starting angular position and valve duration is initialized. That is, intake valves are opened within a minimum opening time and the valve overlap is minimized such that startability of the engine improves.

As stated in detail above, in accordance with the present invention a variable valve duration system gets back to the default angular position rapidly by the restoring force and the mounting structure of a torsional spring at an early stage of an engine starting or stopping and an initial position of valve timing can be regularly started all the time. As a result, startability improves.

For convenience in explanation and accurate definition in the appended claims, the terms “inner” or “outer”, and etc. are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents. 

What is claimed is:
 1. A camshaft-in-camshaft apparatus comprising: a hollow outer shaft having at least one slot formed along a length direction thereof; an inner shaft rotatably inserted inside the outer shaft and having at least one pin hole formed thereon, a position of each of the at least one pin hole corresponding to that of each of the at least one slot; one or more first cam lobes fixedly mounted on an exterior circumference of the outer shaft; one or more second cam lobes fixedly mounted on the inner shaft to be rotatable on the corresponding slot of the outer shaft; a cam phaser changing a phase angle between the outer shaft and the inner shaft by rotating any one of the outer shaft and the inner shaft; and at least one torsional spring mounted between any one of the one or more first cam lobes and any one of the one or more second cam lobes.
 2. The camshaft-in-camshaft apparatus of claim 1, wherein a first cam hole is formed at any one of the one or more first cam lobes and a second cam hole is formed at any one of the one or more second cam lobes, and wherein both ends of one or each of the at least one torsional spring engage respectively with the first cam hole and the second cam hole.
 3. A camshaft-in-camshaft apparatus comprising: a hollow outer shaft having at least one slot formed along a length direction thereof; an inner shaft rotatably inserted inside the outer shaft and having at least one pin hole formed thereon, a position of each of the at least one pin hole corresponding to that of each of the at least one slot; one or more first cam lobes fixedly mounted on an exterior circumference of the outer shaft; one or more second cam lobes fixedly mounted on the inner shaft to be rotatable on the corresponding slot of the outer shaft; and a cam phaser changing a phase angle between the outer shaft and the inner shaft by rotating any one of the outer shaft and the inner shaft, wherein the cam phaser includes a stator connected to one of the outer shaft and the inner shaft and a rotor connected to the other of the outer shaft and the inner shaft, and a torsional spring is mounted between the stator and the rotor.
 4. The camshaft-in-camshaft apparatus of claim 3, wherein a first fixing part is formed or mounted on the stator and a second fixing part is formed or mounted on the rotor, and wherein both ends of the torsional spring are fixed to or engaged respectively with the first fixing part and the second fixing part.
 5. The camshaft-in-camshaft apparatus of claim 4, wherein the first fixing part is a clamp screwed to the stator and the second fixing part is a fixing groove formed in the rotor. 